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Type: Artigo de periódico
Title: Physisorbed water layer formation on fully hydroxylated mesoporous silicas
Author: Collins, KE
de Camargo, VR
Dimiras, AB
Menezes, DTC
da Silva, PA
Collins, CH
Abstract: Kinetic adsorption isotherms were obtained by gravimetric determination of water adsorption into fully hydroxylated mesoporous silicas using samples exposed to controlled humidity air at 22 +/- 2 degrees C. Twenty kinetic isotherms at several relative humidities (11, 33, 43, 51, 75, and 85%) were obtained with 11 different batches of silica using this simple procedure to obtain quantitative information on the formation of H2O adsorbates. The H2O surface concentrations obtained from the plateau data of individual kinetic adsorption isotherms at 43 and 51 % RH, typically precise to about +/- 1%, show that a complete monolayer is formed with negligible second-layer adsorption at these relative humidities. This monolayer has a surface concentration of 7.68 +/- 0.30 mu mol H2O/m(2), which is lower than the quasi-equilibrium concentration at these relative humidities obtained by the conventional equilibrium-isotherm procedure. Comparison with the Kiselev-Zhuravlev concentration of silanol groups on fully hydroxylated silicas (7.6 +/- 0.8 mu mol SiOH/m(2)) confirms 1:1 H2O:SiOH stoichiometry of this monolayer. The presence of partial-layer structures at 2.85 +/- 0.1 and 5.7 +/- 0.1 mu mol H2O/m(2) is suggested by isotherms at 11 and 33% RH, respectively, while a bilayer at similar to 14 +/- 1 mu mol H2O/m(2) is suggested by kinetic isotherms at 75 and 85% RH. (c) 2005 Elsevier Inc. All rights reserved.
Subject: silica
kinetic isotherms
Country: EUA
Editor: Academic Press Inc Elsevier Science
Rights: fechado
Identifier DOI: 10.1016/j.jcis.2005.05.022
Date Issue: 2005
Appears in Collections:Unicamp - Artigos e Outros Documentos

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